Controlled floor jet engine exhaust recirculation

ABSTRACT

Automobile exhaust gases are recycled by means of a bypass duct which receives these gases at a restricted upstream end located within the environment of the hot gases of the exhaust system, passes in heat exchange relationship through the conventional intake manifold hotspot to facilitate heating of the latter, and discharges the hot exhaust gases in an upstream direction with respect to the inlet flow of the fuel-air mixture at a location directly below the throttle valve. The restriction of the upstream end is spaced from the hotspot to minimize heat loss to the latter, such that lead contaminants for example flow in a gaseous phase through the restriction without fouling the same. A bypass control plunger movable in response to the position of the throttle valve is insertable into the restriction to close and simultaneously clean the latter when the throttle valve moves either to its idle or wide open position.

United States Patent Sarto 5] Mar. 7, 1972 [54] CONTROLLED FLOOR JETENGINE EXHAUST RECIRCULATION [52] U.S.Cl. ..l23/1l9 A, 123/127 [51] Int.Cl ..F02m 25/06 [58] FieldofSearch ..123/119 A, 127

[56] References Cited UNITED STATES PATENTS 1,873,174 8/1932 Arthur..l23/1l7A 2,154,417 8/1939 Anderson .....l23/l24 2,643,647 6/1953 Meyeret a1.. .....l23/l27 3,465,736 9/1969 Daigh et al... .,..123/119 A3,542,003 10/1970 Sarto ..123/119 A FOREIGN PATENTS OR APPLICATIONS196,333 4/1923 Great Britain ..123/119A 531,637 1/1941 GreatBritain..123/1l9A Primary Examiner-Wendell E. Burns AttorneyTalburtt & Baldwin[57] ABSTRACT Automobile exhaust gases are recycled by means of a bypassduct which receives these gases at a restricted upstream end locatedwithin the environment of the hot gases of the exhaust system, passes inheat exchange relationship through the conventional intake manifoldhotspot to facilitate heating of the latter, and discharges the hotexhaust gases in an upstream direction with respect to the inlet flow ofthe fuel-air mixture at a location directly below the throttle valve.The restriction of the upstream end is spaced from the hotspot tominimize heat loss to the latter, such that lead contaminants forexample flow in a gaseous phase through the restriction without foulingthe same. A bypass control plunger movable in response to the positionof the throttle valve is insertable into the restriction to close andsimultaneously clean the latter when the throttle valve moves either toits idle or wide open position.

13 Claims, 5 Drawing Figures CONTROLLED FLOOR JET ENGINE EXHAUSTRECIRCULATION RELATED APPLICATION This application is a continuation inpart of my copending application Ser. No. 807,705 filed March 17, 1969,now U.S. Pat. No. 3,542,003.

BACKGROUND AND SUMMARY OF THE INVENTION In the prior art, numeroussystems have been devised to recycle exhaust gas into the fuel-airinduction system of an automobile engine for the purposes of preheatingand vaporizing the incoming air-fuel mixture to facilitate its completecombustion in the combustion zone, for reusing the unignited orpartially burned portions of the fuel which would otherwise pass out theexhaust pipe and into the atmosphere, and for reducing the oxides ofnitrogen emitted from the exhaust system into the atmosphere. It hasbeen found that approximately l5 percent exhaust gas recycling isrequired at moderate loads to substantially reduce the nitrogen oxidecontent of the exhaust gases discharged in the atmosphere, that is, tobelow about 1,000 parts per million.

Although the prior art structures have had the desired effect ofreducing the content of nitrogen oxides in the exhaust by reducing themaximum combustion temperature in consequence of diluting the fuel-airmixture with recycled exhaust gases during certain operating conditionsof the engine, these structures have not been commercially acceptablefrom the standpoints of both cost and operating efficiency and have beencomplicated by the desirability of reducing the recycling duringconditions of both engine idling when nitrogen oxide emission is a minorproblem and wide open throttle when maximum power is required, whileprogressively increasing the recycling of exhaust gases with increasingengine speed during cruising condition or with increasing engine load atpart open throttle. The nitrogen oxide emission is a direct function ofcombustion temperature and for that reason is less critical duringengine idling when the rate of fuel combustion and the consequentcombustion temperature are minimal, and during wide open throttleconditions which are ordinarily of short duration.

in the usual gasoline or hydrocarbon fuel-type engine, fuel combustioncan take place at about l,200 F. The formation of nitrogen oxides doesnot become particularly objectionable until the combustion temperatureexceeds about 2,200 F., but the usual engine combustion temperaturewhich increases with engine load or the rate of acceleration at anygiven speed frequently rises to about 2,500 F. It is known that therecycling of at least l/th and not more than M; of the total exhaustgases through the engine, depending on the load or power demand, willreduce the combustion temperature to less than 2,200 F. The desiredresult is usually obtained with the ordinary engine upon the recyclingof about 15 percent of the total exhaust gases during partially openthrottle as aforesaid.

An important object of this invention is to provide improved meansuncomplicated by moving parts comprising a restricted recycling orbypass duct for recirculating a portion of the combustion products fromthe exhaust system to the inlet system of an automobile engine toovercome or avoid the problems and deficiencies of the prior art, aswell as to achieve a number of important results including preheatingand improved mixing and carburetion of the fuel-air mixture in the inletheader, the reduction of ice formation on the customary throttle blade,and the reduction of nitrogen oxides in the exhaust.

Another object is to provide such a construction wherein the bypass ductextends in heat exchange relationship through the customary hotspot ofthe inlet system and terminates within the induction conduit indirection to discharge hot exhaust gases upstream against the flow ofthe fuel-air mixture in the induction conduit and also against the usualthrottle valve,

thereby to provide simple,'economical and effective means foraccomplishing the foregoing as well as for preheating the throttle andsimultaneously cooling the exhaust gases in the bypass duct below thefuel ignition temperature, and for diluting the fuel-air mixture withsubstantially incombustible exhaust gases to lower the combustiontemperature in the engine and thereby reduce the formation of nitrogenoxides during the combustion process.

Another and more specific object is to provide such an exhaust recyclingsystem wherein the restriction for the bypass duct is adjacent thelatters upstream end within the environment of the hot exhaust gases attemperatures appreciably greater than 700 F. and spaced from the hotspotto minimize heat loss thereto. Such a construction is particularlysuitable for use with fuels containing lead additives to improvecombustion characteristics.

The resulting lead oxides in the exhaust exist in a vapor phase attemperatures above approximately 700 F. The latter temperature is wellbelow the exhaust temperature available but is somewhat higher than theusual temperature of the hotspot, which is continually cooled byimpingement of the comparatively cold inlet fuel and air mixture and thevaporization of liquid fuel droplets within the mixture. Accordingly, bylocating the bypass restriction within the environment of the hotexhaust gases, the temperature of the bypass restriction will preferablybe maintained above 800 F. and the exhaust gases containing lead oxidevapors will pass readily through the hot restriction without condensingthereat. If any lead oxides do condense and deposit within a coolerportion of the bypass duct downstream of the restriction with respect tothe direction of the bypass flow, these deposits will be within anenlarged portion of the bypass duct and will be relatively harmless. Forthis reason also the bypass duct will be comparatively short, so thatthe portion thereof exposed to the comparatively cool inlet fuel and airmixture will only be as long as necessary to assure cooling of the hotexhaust gases sufficiently to prevent ignition of the inlet fuel and airmixture.

By virtue of the foregoing, communication will exist at all timesbetween the exhaust and inlet systems and a portion of the hot exhaustgases will be directed against the throttle valve to prevent or minimizecarburetor icing during fast idling of a cold engine when ice formationis most likely to occur. The downstream opening of the bypass ductopposing the flow of the inlet mixture will be shielded by the throttlevalve at the idle and part open positions, but will be exposed in themanner of a pitot opening to approximately the full velocity pressure ofthe inlet mixture at wide open throttle, whereby the bypass flow may beeffectively reduced at wide open throttle. By suitably determining thesize of the bypass restriction, the bypass flow will be containedapproximately within the limits of more than five percent and less than25 percent, and usually about 15 percent of the total exhaust gases whenthe throttle is partially open and the effective pressure differentialbetween the ends of the bypass duct corresponds to cruising or partthrottle acceleration conditions.

In addition, within the range from idle to light or moderate loadconditions, the total fluid flow through a fixed bypass or recyclingorifice of the type comprising the present invention increases at anygiven engine speed with increasing engine load. For example in aconventional automobile engine, the pressure downstream of the throttlevaries roughly in the neighborhood of from one-half atmosphere duringidling to approximately one atmosphere at wide open throttle, while theexhaust pressure simultaneously varies roughly from one to twoatmospheres. These factors compensate for the increasing combustiontemperature with increasing load and result in a desirable increase inthe effectiveness of the exhaust recycling through the fixed bypassrestriction with increasing load or acceleration.

As the engine load or acceleration decreases and the speed increases tothe cruising condition, the combustion temperature and the pressuredifferential across the fixed bypass restriction, as well as the totalquantity of exhaust gases, decrease and the rate of exhaust recyclingdeclines for improved fuel economy, again as desired because lessrecycling is required to maintain the combustion temperature below thelevel at which nitrogen oxide formation is objectionable. As thepressure differential between the inlet and exhaust headers increaseswith increasing load, the effective resistance of the fixed restrictionto the recycling flow increases because the flow rate variesapproximately as the square root of the pressure differential. Thus atwideopen throttle, the proportion of the total exhaust gases that isrecycled is somewhat less than the proportion recycled at partially openthrottle. This factor also is as desired because the customary excessfuel enrichment at wide open throttle in cooperation with the recycledexhaust gases is adequate to prevent overheating during the combustionprocess and reduce the formation of nitrogen oxides to the tolerablelevel.

Another object is to provide an exhaust recycling system as describedwherein a bypass control valve plunger extends obliquely to the flow ofthe inlet mixture into the downstream opening of the bypass duct andthrough the latters upstream restriction to close the same, and whereinoperation of the plunger is responsive to the position of the throttlevalve, so that the plunger is normally withdrawn from the upstreamrestriction to open the latter, but is moved into the upstreamrestriction to close the same when the throttle valve is at either itsidle or wide open position.

The plunger operating mechanism preferably comprises pressure responsivemeans responsive to the pressure at the customary distributor vacuumadvance port which opens into the inlet header adjacent and at the highpressure side of the leading edge of the usual blade type throttle valvewhen the latter is at its idle position. The high pressure at this portwhen the throttle valve is at either its idle or wide open position istransmitted to the pressure actuated means to move the plunger throughthe upstream restriction of the bypass duct to close the same and at thesame time to maintain the restriction free of exhaust deposits.

By virtue of this construction, the bypass duct may be located to extendthrough the hotspot directly below the throttle valve. The obliqueplunger will extend through the sidewall of of the inlet header to itsoperating means out of the flow path of the inlet mixture.

Other objects of this invention will appear in thefollowing descriptionand appended claims, reference being had to the accompanying drawingsforming a part of this specification wherein like reference charactersdesignate corresponding parts in the several views.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic fragmentarycross-sectional view through an automobile engine induction systemsshowing a bypass duct for recycling exhaust gases.

FIG. 2 is a similar view showing a modification.

FIGS. 3, 4 and 5 show three other modifications embodying a bypasscontrol valve.

It is to be understood that the invention is not limited in itsapplication to the details of construction and arrangement of partsillustrated in the accompanying drawings, since the invention is capableof other embodiments and of being practiced or carried out in variousways. Also it is to be understood that the phraseology or terminologyemployed herein is for the purpose of description and not of limitation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, anapplication of the present invention is illustrated in FIG. 1 by way ofexample with an automobile engine 9 having a carburetor 10 providing theinlet fuel-air induction conduit 11, which comprises the upstreamportion of an inlet header [2 for supplying a combustible fuel and airmixture to the engine cylinders 13, FIG. 3. The carburetor 10 maycomprise any conventional type which has the usual air inlet at theupstream end of the induction conduit II, the usual fuel metering systemand nozzles or jets for supplying idle and operating fuel to the conduitll during various operating conditions and for enriching the fuel supplyduring acceleration and wide open throttle, and the usual automaticchoke (including choke valve 11a) and thermostatic means for controllingidle enrichment and fast idle operation during cold starting conditions.An example of such a carburetor is illustrated by way of example in BallPat. No. 2,966,344, so that the foregoing conventional featuresdisclosed in the latter patent are incorporated herein by reference andare not described in detail.

The downstream portion of the induction conduit ll comprises thecustomary throttle body 16 containing the conventional butterflytypethrottle valve 14. The inlet fuel-air mixture is conducted via theheaders or manifolds 12a and 121;, comprising extensions of the header12, to the left and right banks of cylinders 13 respectively in timedrelation by operation of the inlet valves 18a. After combustion of thefuel-air mixture above the pistons 15, the exhaust gases are conductedin timed relationship by operation of the exhaust valves 18!) to theexhaust manifolds or headers 17, which discharge through a muffler tothe atmosphere.

The left and right manifolds 17 are connected by a crossover conduit 19which conducts the hot exhaust gases into heat exchange relationshipwith portion 20 of the wall of the inlet header 12. The wall portion 20extends transversely to the direction of flow of the inlet mixture andis commonly referred to as the hotspot" which preheats the inlet mixtureand enhances vaporization and mixing of liquid fuel droplets.

A thermostatically controlled valve 21 in one header 17, FIG. 4,controls the flow of hot gases in the crossover conduit 19 to expediteheating of the hotspot 20 during the engine warmup period and to preventoverheating during operation of the engine under load. The structuredescribed thus far may also be conventional.

Associated with the throttle valve 14 and extending through the hotspot20 is a restricted nozzle 22 which extends directly from the exhaustcrossover conduit 19 and has an orifice or restriction 23 at its loweror upstream end opening flush with the interior of conduit 19. Thusnongaseous combustion products cannot readily enter and accumulatewithin the nozzle 22 and clog the bypass system. Where the exhaustcontains appreciable quantities of materials that tend to form gummyresidues upon cooling, as for example in giving up heat to the hotspot20, these residues have less tendency to deposit within the hot passage19 than in the cooler stem of the nozzle 22 which is cooled by the inletfuel and air mixture.

The nozzle 22 is directed toward and terminates adjacent the throttlevalve 14 when the latter is at its idle position shown and directs a jetof exhaust gases in opposition to a jet of inlet gases flowing through arestricted opening 30 in valve 14. The opening 30 may comprise part ofthe idle air supply for the engine, especially during fast idle, and isdimensioned with respect to the dimensions of the exhaust bypass ductsystem to substantially block exhaust recirculation when the throttlevalve 14 is at its warm idle position shown.

As valve 14 progressively opens with increasing engine load, theopposing jets from nozzle 22 and orifice 30 move out of alignment, theeffective pressure differential across orifice. 30 decreases, and thepressure differential across the restriction of nozzle 22 increases, allto the end of increasing the bypass flow or exhaust recirculation fromconduit 19 into conduit ll. Also during part throttle opening, the upperopen end of nozzle 22 is protected by throttle valve 14 from the dynamicor velocity pressure of the inlet gases. At wide open throttle, dottedposition, the upper end of nozzle 22 is exposed to the inlet velocityflow in the manner ofa pitot tube, thereby to oppose and reduce theexhaust recirculation.

The nozzle 22 is suitably secured removably to the hotspot 20, as forexample by the screw connection shown and preferably is formed fromstainless steel to resist corrosion and fouling and, by virtue of theconstruction shown will ordinarily serve properly for'many thousands ofmiles. In the event of eventual plugging of the restriction 23, or inthe event it is IOIO26 OHI desirable to change the latters dimensions toaccommodate changing operating conditions for the engine, the nozzle 22may be removed and replaced through the riser portion of header 12 whenthe carburetor and throttle body 26 are removed.

For operation during normal cruising conditions, the fixed restrictedorifice 23 is dimensioned to enable controlled recycling of a portion ofthe exhaust gases into the inlet header 11 to pass at least five percentand not more than 25 percent of the total exhaust gases, depending uponthe specific engine and its operating conditions. In the usual situationeffective reduction of nitrogen oxides in the exhaust is accomplished byrecycling approximately 15 percent of the exhaust gases as aforesaid,preferably through several nozzles 22, each arranged in the manner ofthe nozzle shown where a multiple barrel carburetor is involved.

ln climatic regions where icing is a problem, each nozzle 22 may beextended into proximity with its associated throttle valve 14 by meansof the low resistance tubular stem or stand pipe shown having a lengthdepending upon the specific geometry and location of the portion of thehotspot through which it extends. Each bypass duct 22 may thus have thesame resistance to gas flow. The flow of the hot exhaust gases throughthe hotspot 20 and nozzle 22 facilitates preheating of the hotspot 20and throttle valve 14 to assure vaporization of the inlet mixture andthe prevention of ice formation adjacent the edges of the throttle valve14. Simultaneously the recycled exhaust gases are cooled below theignition temperature of the combustible inlet mixture. To this end thenonle 22 is preferably of heat conducting material and is sufficientlylong to achieve the necessary heat transfer from the exhaust gases tothe hotspot and inlet mixture. Also by directing the exhaust gasesoppositely to the flow of the inlet mixture, improved breaking up,dispersion and vaporization of liquid fuel droplets are achieved withconsequent improved mixing of the combustible inlet gases and uniformpredictable combustion characteristics within the cylinders 13.

Where the condensation of exhaust matter would otherwise be particularlyobjectionable, as for example with certain fuels containing leadadditives, the structure of FIG. 2 may be employed, wherein acomparatively short stainless steel nozzle 22a is screwed into thehotspot 20 coaxially with the inlet conduit 11 directly below thethrottle valve 14. An enlargement or bolthead 24 of the nozzle 22a has ahexagonal exterior to facilitate assembly and removal of the nozzle 220as described above in regard to FIG. 1 and also serves as a stop tolocate the restriction 23 at a predetermined position below the hotspot20 and within the environment of the hot exhaust gases within passage19. Thus heat loss from the region of the restriction 23 to the coolerhotspot 20 is reduced and the temperature at the restriction 23 willapproximate the temperature of the hot exhaust gases within passage 19which is customarily maintained well above the temperature at which leadcontaminants in the exhaust precipitate. Also by virtue of thecomparatively short length of the nozzle 22a, cooling of the head 24 bythe inlet fuel and air mixture is likewise reduced, and the temperatureof the head 24 may be maintained at approximately the temperature of thehotspot 20, such that fouling of the nozzle 22a and its restriction 23is rendered nominal with many fuels and is less objectionable in anyevent, as compared to conventional bypass conduits employed for exhaustrecycling.

Except for the feature of the opposed jets shown in FIG. 1, the nozzle22a operates substantially in the manner of nozzle 22, the restriction23 being dimensioned to maintain the amount of exhaust recycling withinthe desired range described above. Also as described above, the throttlel4 shields the upper opening of nozzle 22a from the inlet flow of fueland air during idle and part throttle operation to enable a progressiveincrease in the exhaust bypass flow with increasing pressure in conduit19 resulting from increasing engine load,

and to decrease the bypass flow with the consequent decreasing exhaustpressure in passage 19 as the engine attains its cruising speed for anygiven partthrottle opening at wide open throttle the nozzle 22a isexposed to the full velocity pressure of the inlet fuel and air toinhibit exhaust recycling.

FIGS. 3, 4 and 5 show modifications of the present invention wherein theexhaust flow through the bypass nozzle is controlled by a valvemechanism responsive to the position of the throttle valve 14. In FIG. 3a stainless steel nozzle 22!) similar to the nozzle 22 or 22a butprovided with an upwardly enlarging conical opening 31 underlies valve14. A reduced diameter rod or valve element 32a of a reciprocableplunger 32 extends obliquely to the inlet flow of the fuel-air mixturein parallel supported relationship along the conical wall of opening 31,so as to be insertable into the restricted orifice 23. The upper portionof the plunger 32 extends through a bore 33 in the wall of header 12 toa pressure actuated valve'operating mechanism remote from the flow ofthe inlet mixture.

The plunger 32 extends axially through a tubular guide 34 in closelyfitting relationship and is secured at its upper end to a flexiblediaphragm 35 that divides a housing 36 into upper and lower pressurechambers 37 and 38 respectively. The guide 34 screws into the exteriorof bore 33, supports housing 36 at its outer end, and opens into thechamber 38. The latter also opens to the atmosphere via duct 39 whichmay communicate with a source of clean fresh air, as for example at thedownstream side of the conventional carburetor air filter. By virtue ofthe close fit between the plunger 32 and tubular guide 34, a highresistance annular leakage path 39 amounting in essence to a seal isprovided between the chamber 38 and the inlet header l2 downstream ofthrottle valve 14. A coil spring 40 seated between an upper portion ofthe housing 36 and diaphragm 35 urges the latter and plunger 32 downwardfor normally restricting or closing the orifice 23 by insertion of therod or valve portion 32a thereinto.

The chamber 37 is connected by means of a duct 41 with the customaryvacuum advance duct 42 which connects the distributor vacuum advanceport 43 with the customary vacuum actuated mechanism 44 for advancing orretarding the ignition spark distributor in accordance with varyingengine operating conditions. The port 43 opens as is customary adjacentand at the upstream or high pressure side of the upper leading edge ofthe blade of throttle valve 14 when the latter is at its idle positionshown. Accordingly when the throttle valve 14 is at either the idleposition illustrated by solid lines or the wide open positionillustrated by dotted lines, the resulting high pressure at port 43substantially balances the atmospheric pressure in chamber 38 andenables spring 40 to urge plunger 32 downward to restrict or closeorifice 23 and at the same time clear the latter of any deposits thatmight have formed during cold operation of the engine, for example.During part throttle operation, the pressure at port 43 will graduallydecrease as the throttle valve 14 opens from the idle position, wherebythe reduced pressure at port 43 is conducted via conduits 42 and 41 tochamber 37 to withdraw plunger 32 and open orifice 23, as illustrated bythe dotted position, FIG. 4. Simultaneously, as the throttle valve opensfrom the idle position, the resulting reduction in pressure at port 43is communicated to mechanism 44 to actuate the latter to advance thespark distributor in accordance with customary practice.

The nozzle 22b in other respects is substantially the same as nozzle 22or 22a and is releaseably secured within the hotspot 20 coaxially withthe inlet conduit 1]. The latter is not shown to scale in the schematicdrawings and will ordinarily be appreciably oversize with respect to themaximum diameter of the nozzle head 24 to enable installation of thenozzle 22b through the riser portion of the header 12 when thecarburetor and throttle body are removed as above described.

FIG. 4 shows a similar structure where the operating parameters for rodvalve 320 are modified to close orifice 23 only during idle operation.Instead of the spring 40, a spring 40a is employed within chamber 38between a lower portion of housing 36 and diaphragm 35 to urge thelatter upwardly and normally hold the plunger 32 at the open position oforifice 23 as shown. The annular space 39a between plunger 32 and bore33 and also tubular guide 34 is enlarged with respect to thecorresponding space 39 of FIG. 3 to provide an annular passagecommunicating freely between chamber 38 and the inlet header 12downstream of throttle I4. Accordingly, when the latter is at the idleposition, the low pressure downstream of the throttle 14 is communicatedto chamber 38 to move diaphragm 35 and plunger 32 downwardly and insertthe valve extension 32a into the orifice 23 to close or restrict thelatter, dotted position FIG. 4.

During part open throttle operation of the engine, the pressure at port43 and the pressure downstream of throttle valve I4 will tend to be thesame, so that spring 40a will move diaphragm 35 upwardly to open theorifice 23. At wide open throttle, a similar situation will prevail andplunger 32 will remain at the open position shown. Also the nozzle 22bwill no longer be shielded from the flow of the inlet fuel-air mixture,so that this flow will oppose and partially reduce the bypass flow ofexhaust gases into the header 12, thereby to prevent undue dilution ofthe combustible mixture when maximum power is required. On the otherhand, the upward flow of the hot exhaust gases provide effective meansfor enhancing the mixing and vaporization of liquid fuel droplets withthe inlet air to enable increased power at wide open throttle.

FIG. illustrates a structure which operates substantially in the mannerdescribed with respect to FIG. 3, except that in place of the highresistance annular leakage path 39 relied upon in FIG. 3 to separatechamber 38 from the inlet header 12, a flexible sealing diaphragm 45 isprovided to partition chamber 38 into upper chamber 38a and lowerchamber 38b, the former being in communication with the atmosphere viaduct 39 as described above. This structure avoids the necessity ofmaintaining close tolerances between the tubular guide 34 and plunger 32and provides a positive seal to prevent fluid flow between chamber 38band header 12.

Iclaim: I. In an internal combustion engine adapted to use a gasolinefuel containing a lead additive,

B. an exhaust header for discharging the hot combustion products fromsaid engine and having a wall portion comprising a hotspot exposed tothe flow of said fuel-air mixture in said inlet header to heat saidmixture, A. an inlet header for conducting a fuel-air inlet mixture intosaid engine for combustion therein, C. and means for effectivelyinhibiting the formation of oxides of nitrogen during said combustion bylimiting the combustion temperature comprising a bypass duct forconducting hot exhaust gases from said exhaust header into said inletheader, said bypass duct extending through said hotspot in heat transferrelationship to facilitate heating thereof and having I. one end openinginto said exhaust header at a location within the hot exhaust gases andspaced from said hotspot,

2. a second end opening into said inlet header, and

3. a restriction in said bypass duct adjacent the opening of said oneend within said hot gases and spaced from said hotspot to reduce heatloss thereto from said restriction to obtain a temperature at the latterabove the precipitation temperature of lead contaminants in said exhaustgases.

2. In the combination according to claim I, said hotspot extendingtransversely to the flow of said fuel-air mixture in said inlet headerfor impingement of said mixture thereagainst.

3. In the combination according to claim 1, the second end of saidbypass duct opening into said inlet header in an upstream direction withrespect to the flow of said mixture to direct a stream of hot exhaustgases in opposition to said flow to enhance mixing and vaporization ofsaid mixture.

4. In the combination according to claim 3, a throttle valve in saidinlet header upstream of said one end and movable between idle and wideopen positions, said second end opening into said inlet header at alocation increasingly exposed to the opposing flow of said mixture assaid throttle valve moves to its wide open osition.

5. In the com matron according to claim I, a throttle valve in saidinlet header movable between idle and wide open positions, saidrestriction comprising a restricted orifice in said bypass duct, andnormally open valve means responsive to the position of said throttlevalve for restricting said orifice when said throttle valve is adjacenteither its idle or wide open position.

6. In the combination according to claim I, said restriction beingspaced within said exhaust header from said hotspot sufficiently tomaintain an operating temperature at said restriction above 700 F.

7. In the combination according to claim I, said bypass duct having acomparatively short length on the order of magnitude of the wallthickness of said hotspot and extending directly through said hotspotand terminating within said inlet header proximate the surface of saidhotspot exposed to said inletv mixture.

8. In the combination according to claim 7, said bypass duct beingcomparatively resistance free to the flow of exhaust gases therethroughdownstream of said restriction.

9. In the combination according to claim 7, the opening of said bypassduct enlarging downstream of said restriction.

10. In the combination according to claim 9, a throttle valve in saidinlet header movable between idle and wide open positions, a valveplunger within said inlet header movable obliquely within the enlargingdownstream opening of said bypass duct, and means responsive to theposition of said throttle valve for normally maintaining said plungerout of said restriction and for moving said plunger into saidrestriction when said throttle valve is adjacent either its idle or wideopen position.

11. In the combination according to claim I, the opening of said bypassduct enlarging conically downstream of said restriction, a throttlevalve in said inlet header movable between idle and wide open positions,a valve plunger reciprocable along the conical surface of the conicallyenlarging opening of said bypass duct and within said restriction toreduce the opening of the latter, and plunger operating means responsiveto the position of said throttle valve for normally maintaining saidplunger out of said restriction and for moving said plunger into saidrestriction when said throttle valve is adjacent either its idle or wideopen position.

12. In the combination according to claim 11, said second end of saidbypass duct opening into said inlet header at a location shielded fromthe opposing flow of said mixture by said throttle valve when the latteris at its idle position and exposed to said opposing flow when saidthrottle valve moves to its wide open position.

13. In the combination according to claim 11, said bypass duct beinglocated centrally with respect to the flow of said mixture downstream ofsaid throttle valve, said plunger having a remote end out of said flow,and said plunger operating means engaging said remote end to operatesaid plunger.

1. In an internal combustion engine adapted to use a gasoline fuelcontaining a lead additive, B. an exhaust header for discharging the hotcombustion products from said engine and having a wall portioncomprising a hotspot exposed to the flow of said fuel-air mixture insaid inlet header to heat said mixture, A. an inlet header forconducting a fuel-air inlet mixture into said engine for combustiontherein, C. and means for effectively inhibiting the formation of oxidesof nitrogen during said combustion by limiting the combustiontemperature comprising a bypass duct for conducting hot exhaust gasesfrom said exhaust header into said inlet header, said bypass ductextending through said hotspot in heat transfer relationship tofacilitate heating thereof and having
 1. one end opening into saidexhaust header at a location within the hot exhaust gases and spacedfrom said hotspot,
 2. a second end opening into said inlet header, and3. a restriction in said bypass duct adjacent the opening of said oneend within said hot gases and spaced from said hotspot to reduce heatloss thereto from said restriction to obtain a temperature at the latterabove the precipitation temperature of lead contaminants in said exhaustgases.
 2. a second end opening into said inlet header, and
 2. In thecombination according to claim 1, said hotspot extending transversely tothe flow of said fuel-air mixture in said inlet header for impingementof said mixture thereagainst.
 3. In the combination according to claim1, the second end of said bypass duct opening into said inlet header inan upstream direction with respect to the flow of said mixture to directa stream of hot exhaust gases in opposition to said flow to enhancemixing and vaporization of said mixture.
 3. a restriction in said bypassduct adjacent the opening of said one end within said hot gases andspaced from said hotspot to reduce heat loss thereto from saidrestriction to obtain a temperature at the latter above theprecipitation temperature of lead contaminants in said exhaust gases. 4.In the combination according to claim 3, a throttle valve in said inletheader upstream of said one end and movable between idle and wide openpositions, said second end opening into said inlet header at a locationincreasingly exposed to the opposing flow of said mixture as saidthrottle valve moves to its wide open position.
 5. In the combinationaccording to claim 1, a throttle valve in said inlet header movablebetween idle and wide open positions, said restriction comprising arestricted orifice in said bypass duct, and normally open valve meansresponsive to the position of said throttle valve for restricting saidorifice when said throttle valve is adjacent either its idle or wideopen position.
 6. In the combination according to claim 1, saidrestriction being spaced within said exhaust header from said hotspotsufficiently to maintain an operating temperature at said restrictionabove 700* F.
 7. In the combination according to claim 1, said bypassduct having a comparatively short length on the order of magnitude ofthe wall thickness of said hotspot and extending directly through saidhotspot and terminating within said inlet header proximate the surfaceof said hotspot exposed to said inlet mixture.
 8. In the combinationaccording to claim 7, said bypass duct being comparatively resistancefree to the flow of exhaust gases therethrough downstream of saidrestriction.
 9. In the combination according to claim 7, the opening ofsaid bypass duct enlarging downstream of said restriction.
 10. In thecombination according to claim 9, a throttle valve in said inlet headermovable between idle and wide open positions, a valve plunger withinsaid inlet header movable obliquely within the enlarging downstreamopening of said bypass duct, and means responsive to the position ofsaid throttle valve for normally maintaining said plunger out of saidrestriction and for moving said plunger into said restriction when saidthrottle valve is adjacent either its idle or wide open position.
 11. Inthe combination according to claim 1, the opening of said bypass ductenlarging conically downstream of said restriction, a throttle valve insaid inlet header movable between idle and wide open positions, a valveplunger reciprocable along the conical surface of the conicallyenlarging opening of said bypass duct and within said restriction toreduce the opening of the latter, and plunger operating means responsiveto the position of said throttle valve for normally maintaining saidplunger out of said restriction and for moving said plunger into saidrestriction when said throttle valve is adjacent either its idle or wideopen position.
 12. In the combination according to claim 11, said secondend of said bypass duct opening into said inlet header at a locationshielded from the opposing flow of said mixture by said throttle valvewhen the latter is at its idle position and exposed to said opposingflow when said throttle valve moves to its wide open position.
 13. Inthe combination according to claim 11, said bypass duct being locatedcentrally with respect to the flow of said mixture downstream of saidthrottle valve, said plunger having a remote end out of said flow, andsaid plunger operating means engaging said remote end to operate saidplunger.